GENETIC-STRUCTURE OF THE DNAA REGION OF THE CYANOBACTERIUM-SYNECHOCYSTIS SP STRAIN PCC6803

We have cloned and sequenced the dnaA region of Synechocystis sp, stra in PCC6803, a bacterium with a light-dependent cell cycle. The dnaA ge ne product, DnaA, is the central factor for replication initiation in bacteria. The deduced amino acid sequence of the protein encoded by th e cyanobacterial dnaA gene is 45% identical to DnaA of Bacillus subtil is and fits very well into the homology pattern of the known eubacteri al DnaA proteins. The genetic environment of the Synechocystis sp, str ain PCC6803 dnaA gene is completely different from the one in other eu bacteria, An open reading frame of unknown function, orf134, was detec ted upstream of dnaA. The purT gene homolog encoding the glycinamide r ibonucleotide transformylase T starts about 200 bp away from this open reading frame in the opposite direction. Downstream of the dnaA gene we detected the start of the psbDC operon, which codes for the photosy stem II reaction center proteins D2 and CP43 that are involved in the positioning of chlorophyll a.